The Boy Mechanic Part 104

** Using Sandpaper [376]

Sandpaper may be kept from slipping under the hand by chalking the back.

** An Interesting Electrical Experiment [377]

Anyone possessing a battery having an electromotive force of from 4 to 20 volts can perform the following experiment, which is particularly interesting on account of the variation of results with apparently the same conditions.

Immerse two pieces of bra.s.s in a strong solution of common salt and water. Connect one piece to the positive wire and the other to the negative, taking care that the bra.s.s pieces do not touch each other.

After the current has pa.s.sed one

[Ill.u.s.tration: How Wires are Connected]

or two minutes, the solution will become colored, and if the process is continued a colored pigment will be precipitated. The precipitate varies considerably in color and may be either yellow, blue, orange, green or brown, depending on the strength of the current, the strength of the solution, and the composition of the bra.s.s.

** Novelty Chain Made from a Match [377]

The accompanying engraving shows what is possible to do with a penknife.

[Ill.u.s.tration: Lay a Match on the Picture]

A small chain composed of several links was cut from the wood that forms the match.

** Keeping Doors Closed [377]

Gla.s.s doors in bookcases may be kept from swinging open by boring a hole, about 1/4 in. deep, either at the top or bottom in the edge of the door, 2 in. from the closing edge, and inserting an ordinary cork, allowing a small portion to project and rub on the facing.

** Restoring Broken Negatives [377]

Whoever has the misfortune to break a valuable negative need not despair, for the damage can be repaired most effectively. In case the negative be broken into many pieces, take a clean gla.s.s, the same size as the broken negative, and put upon this the pieces, joining them accurately, says Camera Craft. Put another clean gla.s.s on top of this and bind the three together with pa.s.se-partout binding or gummed strips of ordinary paper, as one would a lantern slide, and cover the gla.s.s edges.

Next make a transparency of this--in the camera, of course--and if it is done right, the positive will only show the cracks as dark and light lines. The

[Ill.u.s.tration: Before and After Mending]

dark lines are removed with the etching knife and the light ones with the retouching pencil. From this transparency another negative can be made, or as many negatives as necessary, by either contact or in the camera, and if the work on the gla.s.s positive was done carefully, no trace of the break should be seen on the finished negative. If the negative is broken in two or three larger pieces only, a contact positive may be made in the printing frame without binding, by using a clean gla.s.s in the latter, upon which the pieces are put together, face up, and a dry plate exposed in contact with them in the dark room. The accompanying engravings show a print before and after repairing a broken negative in this manner.

** Coin and Tumbler Trick [378]

The accompanying sketch shows how a good trick may be easily performed by anyone. Lay a piece of

[Ill.u.s.tration: This Is a Good Trick]

heavy paper that is free from creases on a board or table. Secure three tumblers that are alike and stick a piece of the same heavy paper over the openings in two of them, neatly tr.i.m.m.i.n.g it all around the edges so as to leave nothing of the paper for anyone to see. Make three covers of paper as shown in Fig. 1 to put over the tumblers. Place three coins on the sheet of paper, then the tumblers with covers on top of the coins, the unprepared tumbler being in the middle. Now lift the covers off the end tumblers, and you will see that the paper on the openings covers the coins.

Replace the covers, lift the middle one, and a coin will be seen under the tumbler, as the opening of this tumbler is not covered.

Drop the cover back again and lift the other tumblers and covers bodily, so that the spectators can see the coins, remarking at the same time that you can make them vanish from one to the other. The openings of the tumblers must never be exposed so that any one can see them, and a safe way to do this is to keep them level with the table.

** Another Way to Renew Dry Batteries [378]

There are many methods of renewing dry batteries, and I have used several of them, but I found the following the best: Remove the paper cover and with a 1/4-in. drill make about six holes around the side of the zinc, about 1/2 in. from the bottom. Then drill another row of holes about half way up the side and put the battery to soak in a solution of sal ammoniac for 48 hours. Then remove and plug the holes up with hard soap, and replace in the paper box, when it will give nearly as strong a current as when new.

** Simply Made Wire Puzzle [378]

The object of this simply made wire puzzle is to get the ring off, which is not easy unless you know how. To do so it is necessary to move the triangle with ring to one of the hinge joints and fold the puzzle. Then slip the ring off the triangle over the hinge joint and it will slip all around and off at the other hinge.

[Ill.u.s.tration: Puzzle]

** p.r.o.nunciation [378]

Diabolo is p.r.o.nounced Dee-ab-lo.

** Repairing Box Cameras [379]

In repairing the inner part of box cameras which have been broken loose, use a binding of strong black cloth well glued in place.

This will materially strengthen the joints where the wooden pieces are so thin that it is impossible to use brads in holding them together.

Do not forget to thoroughly clean all the old glue or cement from the joints with a rasp or sandpaper before attempting a repair.

** A Fishhook Box [379]

A box that may be used to hold fishhooks, sinkers, matches or any small articles, can be made from two empty shotgun cartridges as shown in the sketch. The paper is cut from the bra.s.s part of one sh.e.l.l at the place marked A, Fig. 1, and the bra.s.s part, Fig-. 2, is used for a cap on the other

[Ill.u.s.tration: Made of Shotgun Sh.e.l.ls]

sh.e.l.l (Fig. 3). Coating the box with sh.e.l.lac will improve its appearance.

--Contributed by Abner B. Shaw, N. Dartmouth, Ma.s.s.